Abstract: A hash function used for content addressing is different from the hash function used for content verification. Adding a file to a database involves storing both hash function values in a table as pair. Verifying the integrity of a file believed to be a duplicate in a database, or when retrieving a file, makes use of the verification hash function. Files can be continuously checked. A multi-level database can be used. A second hash function can be added to an existing system. A verification hash function can be upgraded and more than one content verification hash function can be used. In a variation, a random number generator is used instead of a hash function for content addressing; the verification hash function is also used. Files addressed using a random number are added or retrieved from a database and their verification hash values are checked. Time stamps and digital signatures are used for security.

Abstract: Content-based addressing is used to navigate forward, backward and in a circular fashion through documents in a content space. To enable backward navigation, a descriptor file is created for a new version that contains not only a message digest for the new version, but also a message digest of the older document. A message digest is created for the descriptor file. A user navigates backward starting with the message digest of the descriptor file. To enable forward navigation, a mapping table maps a message digest of an older document into the message digest of the new version. A high-level descriptor file contains the message digest of the original document and the message digest of the mapping table. The message digest of the high-level descriptor file is returned to the user. A user navigates forward starting with the high-level descriptor file message digest.